Nassau, Bahamas - King Charles III begins a tour of the Caribbean on Tuesday amid growing calls to apologize and pay reparations for enslavement, which he has called the "darkest days" of British history.

The 77-year-old king, who is receiving treatment for an undisclosed form of cancer, will embark on a jam-packed trip taking in three countries in nine days.

He will first make solo visits to the Bahamas and Guyana, before being joined by his wife, Queen Camilla, for the final leg in Antigua and Barbuda, where he will address the bi-annual meeting of Commonwealth heads of government (CHOGM).

The program will "not shy away from 'the darkest days of our past,' as His Majesty has described them," a Buckingham Palace spokesperson said, ahead of the tour of the former colonies.

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Several of them have demanded the king take the next step in making amends for colonialism and transatlantic enslavement, which he and his ancestors have profited off for centuries.

Last month, Jamaica – where Charles is head of state – filed a petition in an appeals court in London "to advance Jamaica's push for reparations for the African ancestors who suffered under hundreds of years of enslavement."

Few in royal circles will have forgotten a 2022 trip to Jamaica by Prince William, when he and Princess Catherine were met with anti-monarchy protests and calls for reparations.

Guyana's President Irfaan Ali, who is set to meet with Charles during his visit, told ITV News the king's recognition of the "darkest days" was just the "first step."

"Now, moving to the apology is the next step," said Ali, demanding accountability from the former empire which he said "exploited the region," "destroyed lives," and "created underdevelopment."

No monarch has yet formally apologized for Britain's central role in chattel slavery, and London has balked at the idea of financial compensation.

Commonwealth Secretary-General Shirley Ayorkor Botchwey told Sky News ahead of the meeting of the group's leaders from November 1 to 4, that it "wouldn't hurt" for the king to apologize.

Botchwey also said the "time has come" to discuss reparations, in the form of financial payments or otherwise.

Buckingham Palace has insisted Charles' royal tour is an opportunity for the Caribbean nations to look forward and address pressing issues like climate change.

He will also engage in various cultural events and meet young leaders, as well as attending independence celebrations in Antigua and Barbuda.

According to Botchwey, the Commonwealth, which includes 56 member countries with the king at its helm, is an important anchor in a "world that is almost spinning out of control."

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"This CHOGM is going to be one like never before," the secretary-general told AFP in an interview, with the meeting in St. John's set to focus on investment and trade opportunities for member countries.

Charles will meet organizations working in the environmental field, including a coral restoration project in Antigua and Barbuda and rainforest conservation in Guyana.

"Many of these countries that are affected by climate are not polluters, and yet they feel the brunt of the effects of climate," said Botchwey, adding that the CHOGM summit will also touch upon climate resilience schemes.

While she refused to elaborate on whether the UK government and royals should pursue reparations for slavery, she said the issue would be on the table in St. John's.

"What will happen in Antigua and Barbuda may be that the leaders will have a discussion on reparatory justice," said Botchwey, adding the Commonwealth would "support" countries in the talks.

"The Commonwealth has been an organization that has never shied away from difficult situations," she added.